Barley extrudates modulate the gut microbiome–metabolome axis in vitro through β-glucan fermentation and polyphenol biotransformation

digestion-colonic fermentation model. The gastrointestinal fate of β-glucans and phenolics, short-chain fatty acids production, phenolic metabolite formation, and gut microbiota composition were assessed. After digestion, substantial amounts of β-glucans and phenolics remained in the non-bioaccessible fraction, supporting their relevance as substrates for colonic fermentation. During fermentation, the β-glucan-rich genotypes Annapurna® and Hilose® showed the strongest butyrogenic response, while the purple-grain genotype DHL-151340, characterized by a flavone- and anthocyanin-rich profile, showed an earlier and more pronounced accumulation of low-molecular-weight phenolic catabolites. Compared with the control, barley extrudates induced time-dependent shifts in microbiota composition, although community profiles tended to converge at later fermentation stages. Overall, genotype- and processing-driven differences translated into distinct fermentation and phenolic biotransformation footprints, highlighting the relevance of barley matrix composition in shaping the colonic fate of cereal bioactive compounds.